142 DR. J. BRAXTON HICKS ON UNDESCRIBED SENSORY ORGANS IN INSECTS. 
In the palpi of all Diptera formed on the same plan as in Musca, I have found these 
structures existing, varying indeed in numher and size. I have also found them in 
Eristalis tenax. 
In many of the Diptera (Musca, Mesembrinum, for instance, and Plies of similar con- 
struction), a group of organs of a somewhat similar character is to be found on the tips 
of the piercers ; in some there are as many as twenty on each side of the middle line, two 
large ones generally . being situated at the apex. In Tabanus bovinus the tip of the 
central portion or piercers possesses as many as twenty, apparently having the same 
structure as those in the Hymenoptera, to be immediately described. 
I have found similar organs on or about the palpi of some of the Hymenoptera, as 
Vespa, Odynerus, Apis, Bombus, Megachile, Nomada, &c. I have, in PI. XVIII. fig. Q, 1, 
figured these in Vespa Crabro. They are situated at the basal joint of the labial palpi, 
about twelve in number, and in the same joint of the maxillary palpi, but fewer and 
more scattered. In Vespa vulgaris their diameter is 1 g 70 inch. In fig. Q, 2, I have 
given an enlarged view of one, — (2) showing a section in which the nerve (a) is seen 
expanding on the inner surface of the covering-in membrane, (3) as seen from above. 
In Odynerus muraria and O Antilope, for instance, they are found also on the centre 
of the base of the labium. 
In Apis mellifica these organs, instead of being placed on the first joint of the labial and 
maxillary palpi, are close to the origin of the palpus. I have shown these at PI. XVIII. 
fig. It, 1 a, 2 a. If we examine the apex of the labial palpi of this Bee, we shall find three 
or four structures somewhat similar, but having a few papillae at the surface. They are 
situated among the hairs, and are represented at PI. XVIII. fig. E, 3 a. In the Megachile 
(Leaf-cutting Bee) they are very similarly situated, but on the base of the tongue, and on 
the basal joint of its palpus, and a few scattered over the second joint (PI. XIX. fig. A, 1). 
In Nomada succmcta I can find them only on the base of the labial palpi, and one on 
the distal end of each segment of the same palpi, which latter are of much larger size 
(PI. XIX. fig. B, a) . 
This will suffice to point out the kind of structure to be found on or about the palpi ; 
to all of them a bundle of nerves can be seen proceeding. 
In Dyticus marginalis I have observed a few organs on the maxillary palpi, situated in 
an oblique row (PI. XIX. fig. E, la & 3), of apparently similar nature to the structures 
which I have observed on the antennas of that insect (in the second paper read before the 
Linnean Society, May 1859). They are shown enlarged at fig. E, 3. 
A group of similar structures is to be found in some of the Arachnida, as Arania, 
Tegenaria, on the under surface of the maxillse, extending lengthwise along the middle 
on a space nearly devoid of hairs. They are the only organs which I have been able to 
meet with in that tribe ; but as the habits of the Arachnida show them to be chiefly 
dependent on sight for their guidance in obtaining supplies of food, we probably might 
not expect to find a large development of these organs, or others I am about to mention . 
In the palpi of Lepidoptera I have observed a peculiar structure, which I cannot find 
noticed by any one, and which differs much from the other I have described. 
The structure in question consists of a depression on the apex of the terminal joint, 
